Analysis of Benzidine and Dichlorobenzidine at Trace Levels in Water by Silylation and Gas Chromatography–Mass Spectrometry

Conditions for silylation of benzidine (BZ) and 3,3′-dichlorobenzidine (DCBZ) have been optimized. Reactivity, repeatability, and derivative stability were compared for the silylating reagents N-Methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) and N-Methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide (MTBDMSTFA) and the catalysts 3% trimethylsilylimidazole (TMS-I) and 0.3% NH₄-I–dithioerythritol. The results showed that derivatization with MTBDMSTFA/NH₄-I containing 0.1 mg dithioerythritol was superior to other methods. The silylation conditions selected were reaction with (MTBDMSTFA)–NH₄I, 1000:3, with catalysis by dithioerythritol, at 80 °C for 80 min. The TBDMS derivatives of BZ and DCBZ had very good chromatographic properties and very sensitive detection was achieved by gas chromatography with electron-impact ionization mass spectrometry (GC-EIMS). Simultaneous determination of BZ and DCBZ in water was developed on the basis of the TBDMS derivatives. Deuterated BZ (d8-BZ) was chosen as internal standard (IS) for analysis of water samples. BZ and DCBZ were extracted from water at pH 8.5 with dichloromethane and the extract was then dried and silylated. Recoveries of BZ and DCBZ were approximately 102 and 103% at a concentration of 2.0 ng mL⁻¹. The coefficients of variation for BZ and DCBZ were less than 9 and 4% at concentrations of 0.2 and 0.5 ng mL⁻¹, respectively. The method detection limits for 200 mL water were 0.004 ng mL⁻¹ for BZ and 0.02 ng mL⁻¹ for DCBZ.